1. Field of the Invention
The present invention relates to an optical lens system suitable for use in forming a concentric interference pattern, as well as to a positional measurement system for measuring a one-dimensional, two-dimensional, or three-dimensional position of an object by utilization of the concentric interference pattern. In addition to being utilized for positional measurement, the present invention can also be utilized as, e.g., a pointer, a device for inputting a distance image, and a positional information system.
2. Description of the Related Art
Measuring the orientation of an object is generally not easy. For example, a method for measuring the pointing direction of a pointer includes a method for photographing, through use of two cameras, two LED light sources attached to the pointer, computing positions of the respective LED light sources in accordance with the principle of triangulation, and determining the orientation of the pointer. However, the actual pointer has a length of about 10 cm. When the cameras and the pointer are spaced several meters apart from each other, positional accuracy becomes deteriorated. Hence, the direction of the pointer cannot be measured accurately. In the case of triangulation, two or more cameras must be able to photograph a single point at all times. In reality, in some cases one of the cameras is blocked by another of the cameras, and performing measurement at all times is not easy. In the case of triangulation using two or more cameras, positions of the cameras must be corrected after the axial directions of the respective cameras and the intervals between the cameras have been arranged accurately. This raises a problem of a round of these operations being troublesome.
Another currently-proposed technique is for detecting, through use of a CCD camera attached to a projector, a point indicated by a laser pointer and moving a cursor to coordinates of that point. However, this method can be utilized for only the case of a projection-type display and has a problem of being unsuitable for an ordinary display and lacking general versatility. Yet another method is a pointer of gyro type. This method is for measuring the amount of three-dimensional rotational movement of the gyro pointer by utilization of the gyro serving as an angle sensor and sending the amount of movement to a computer by wireless communication, to thus move the cursor. However, this method is for measuring only the amount of rotational movement of the gyro pointer. The direction of a vector actually indicated by a human is totally irrelevant to the position of the cursor, thereby raising a problem of difficulty in ascertaining an indicated position. There is also proposed still another method for measuring the three-dimensional position of a pointer by utilization of light or ultrasonic waves, to thus input the three-dimensional position into a computer. However, in any case, the direction of a vector indicated by the pointer is unknown, and the “function of an indicating point which is an extension of a finger or a hand” cannot be fulfilled.
An optical interference method utilizing optical interference is often used as a method for accurately measuring a position. The optical interference measurement method includes a method for splitting the light exiting a laser light source into two beams by a beam splitter. One of the split beams is radiated on an object, and the other beam is emitted to a mirror as reference light so as to return along the original light path. The light reflected from the object is superimposed on the reference light, to thus cause interference. This method yields an advantage of the ability to measure a position and displacement by resolving power which is equal to or less than a wavelength. However, this method requires optical components, such as a beam splitter or a reflection mirror, and suffers a problem of involving a large number of components and a high cost. When an optical interference measurement method is applied to an object which moves, there is a necessity to automatically trace an object and continuously radiate light, thereby yielding a disadvantage of a further increase in cost.
A laser gauge interferometer capable of reducing the number of components is described in JP-B-4-8724.
The interferometer uses a gradient index lens. This gradient index lens is formed such that the refractive index of an optical glass rod becomes lower as the rod departs from the center axis by ion diffusion. A gold-evaporated semi-transparent mirror is formed on an entrance-side end of the gradient index lens and an exit-side end of the same. Interference arises between direct light emitted from a laser and reflected light which again enters the gradient index lens after having undergone reflection on a semi-transparent mirror of the gradient index lens and reflection on the exit-end surface of the laser. The number of components of this interferometer can be reduced to a certain extent in comparison with the previously-described optical interferometer. However, a gradient index lens must be prepared, and a semi-transparent mirror must be formed. Hence, the interferometer cannot be said to be satisfactory in terms of cost.
Another optical interference measurement method employs a diffraction grating or a slit. In order to cause optical interference through use of a diffraction grating or a slit, a diffraction grating or a slit must be formed at pitches essentially equal to a wavelength, and hence micromachining is required. Therefore, there arises a problem of components being expensive. In contrast, when a slit is used, the quantity of light passing through the slit is substantially diminished even when the slit is exposed to a laser beam, and there arises a problem of difficulty being encountered in utilizing the slit in an ordinary environment.
An optical projector is attached to an object as means for measuring the orientation of the object. A concentric circular pattern is projected on a wall from the projector. The concentric patterns are detected by sensors, such as image sensors, provided on the wall, thereby computing the center of the concentric circles. Thus, the orientation of the object can be measured. In this case, focus must be obtained such that an interference pattern does not become blurred in accordance with a distance between the optical projector and the wall. When the object moves dynamically, there arises a problem of focusing lagging behind movement. An automatic focusing mechanism, or the like, is also required, which in turn adds to costs.
As mentioned above, under present circumstances, there is no pertinent means for accurately measuring the orientation and direction of the moving object.
According to a conventional method for photographing an object with two cameras which act as means for measuring the orientation of the object, the positional accuracy of measurement is low, and the direction of the object cannot be measured accurately. Moreover, processes for arranging two cameras and correcting positions of the cameras are troublesome. A conventional optical interference technique which enables highly-accurate positional measurement suffers problems, that is, high costs of components of an interference optical system, high precision required for assembly, a larger number of components, a large number of assembly steps, and the technique being unsuitable for positional measurement of a moving body. Moreover, the method for projecting a concentric circular pattern by a projector suffers problems, that is, consumption of time to obtain focusing, a bulky size, a heavy weight, and high power consumption.